Getter systems comprising an active phase inserted in a porous material distributed in a low permeability means

ABSTRACT

Getter systems are provided having a phase active in the sorption of gas, inserted in the pores of a porous material. The porous material is, in turn, dispersed in a polymeric means having a low permeability to the gas to be sorbed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Section 371 of International Application No.PCT/IT2006/000540, filed Jul. 18, 2006, which was published in theEnglish language on Feb. 1, 2007, under International Publication No. WO2007/013119, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to getter systems comprising a phaseactive in gas sorption inserted in a porous material distributed in alow permeability means.

Getter materials and systems are widely used in industry in allapplications where it is necessary to maintain a vacuum, to control thecomposition of the gaseous atmosphere through the sorption of traces ofundesired gases or to protect devices sensitive to particular gaseouscontaminants.

Getter materials widely used for such purposes are porous materials,such as active carbons, particularly useful for the sorption of organicsubstances, or zeolites, silica or alumina, useful for the sorption ofgaseous molecules of small size. Another class of particularlyinteresting compounds is comprised of anhydrous chemical desiccants,specific for moisture sorption, such as the oxides of alkaline-earthmetals, or some hygroscopic salts such as chlorides (e.g., calciumchloride, CaCl₂), perchlorates (e.g., magnesium perchlorate, Mg(ClO₄)₂),or sulphates (e.g., calcium sulphate, CaSO₄).

One problem common to many of these materials is that they are generallyin the form of powders without cohesion sufficient to form compactbodies. This is particularly true in the case of desiccants aftermoisture sorption. This is a relevant problem, as in almost all foreseenindustrial applications the absence of free particles is required.

The problem is in some cases tackled by inserting the getter materialsinside permeable containers (e.g., non-woven fabric envelopes, as shownfor instance in U.S. Pat. No. 4,668,551 directed to insulating panels).

Another possible approach to the problem is to distribute the gettermaterial inside a dispersing matrix, capable of retaining the getterparticles in a fixed location while letting the gases pass towards thegetter itself. Examples of this second solution are set forth innumerous documents. Japanese patent application publication JP 60-132274discloses desiccant materials dispersed in a silicone matrix; U.S. Pat.No. 3,704,806 discloses desiccant compositions comprising zeolitesdispersed inside a matrix formed of a thermosetting polymer, such as theepoxy resins; U.S. Pat. No. 4,081,397 discloses a desiccant systemcomprising particles of an oxide of an alkaline-earth metal dispersed inan elastomeric polymer; U.S. Pat. No. 5,304,419 discloses desiccantcompositions comprising a desiccant material dispersed in a matrix thatcan be formed of silicone, polyurethanes or similar polymers; U.S. Pat.No. 5,591,379 discloses desiccant compositions comprising a desiccantselected from zeolites, alumina, silica gel, alkaline-earth metaloxides, and alkaline metal carbonates, dispersed in a matrix of porousglass or ceramic; U.S. Pat. No. 6,226,890 B1 discloses desiccant systemswherein a desiccant material (e.g., an alkaline-earth metal oxide) isdispersed in a polymer, such as silicones, epoxides, polyamides,polymethylmethacrylates or others, which in the patent is said to havethe property of not reducing or even increasing the sorption speed ofwater by the desiccant material; U.S. Pat. No. 6,819,042 B2 disclosesdesiccant systems comprised of a desiccant material dispersed in aresin, e.g., a polyethylene, polypropylene, polybutadiene, orpolyisoprene resin; finally, U.S. Pat. No. 6,833,668 B1 discloses asystem to damp the impact of moisture on the sensitive components oforganic light emitting displays (OLEDs), which is based on animpermeable resin barrier containing a desiccant powder, wherein thebarrier function of such a system is pointed out by use as a means forsealing OLED cavities.

One limit that is common to many of the systems disclosed in thesepatents, whether based on dispersing matrices permeable to gases orhaving poor permeability, is that, due to the reaction with the gas tobe sorbed, the getter material generally undergoes structural andmorphological modifications, e.g. swellings, which, particularly in thecase of desiccants, can be considerable. The presence of a matrixsurrounding the particle of getter material can hinder thesemorphological modifications and inhibit or delay the gas sorptionreactions.

In addition, some industrial applications may pose other requirements togetter systems. For instance, OLEDs of the latest generation require agetter system that is transparent and has constant optical propertiesthroughout the whole life of the device, that is, soon after manufacture(when the getter material has not yet sorbed moisture, except forminimum amounts), near the end of the life of the device (when thegetter device has already sorbed relatively large amounts of moisture,even up to saturation of the system) and also at intermediate steps ofthe OLED life, that is when the various getter particles dispersed inthe matrix have sorbed different amounts of moisture. The differentlevels of moisture absorbed by getter particles during the OLED life canchange optical properties of the system, such as its light transmissionor refractive index, thus impairing the quality of the display. Theproblem is discussed, for example, in U.S. Pat. No. 6,465,953 disclosinga getter system for OLED, comprised of getter particles in a transparentmatrix, wherein the particles have sufficiently small size not tointeract with the luminous radiation. Given the importance of thisapplication, in order to illustrate the uses of the getter systems ofthe invention, reference will be particularly made to the use in OLEDs,but the getter systems of the invention are of a general use and may bealso used in other applications.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a low permeabilitygetter system capable of sorbing permeating gaseous species.

According to the present invention, this and other objects are obtainedwith a getter system comprising:

a polymeric means poorly permeable to the gases to be sorbed;

a powder of a porous material distributed in the polymeric means; and

a phase active in the sorption of one or more gases in the pores of theporous material.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown. In thedrawings:

FIG. 1 is a schematic, broken-away, perspective view of a getter systemaccording to an embodiment of the invention;

FIG. 2 is an enlarged, schematic, sectional view of one particle ofpowder of the porous material used in an embodiment of the invention;and

FIGS. 3 a and 3 b are further enlarged, schematic, sectional views,illustrating the gas sorption reaction that takes place inside the poresof the particle of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

The getter systems of the invention are differentiated from those of theprior art in that the material active in the sorption of gases is notdirectly dispersed in the matrix, but is present inside the pores of a“guest” phase, the latter being in the form of powders dispersed in thematrix. This feature ensures that the physical properties of the systemare essentially invariant with respect to gas sorption. For example,although the active material may undergo morphological modificationsduring gas sorption, these modifications are not transmitted outside theindividual porous particle, so that the interactions between the latterand the environment (the matrix) are not modified.

With respect to the known getter systems, in addition to theabove-illustrated difference, the systems of the invention offer anumber of advantages. First, if the dispersed porous material has welldefined geometric features (e.g., in the case where it is a natural orsynthetic zeolite, fullerenes or the like), it is capable oftransforming a reversible reaction or process into a non-reversiblereaction or process, due to the steric hindrance of the products and/ordue to particularly high chemical forces exerted against the pore walls,such that the reaction products are tightly held in the pores. Inaddition, the porous material may receive a catalyst in addition to theactive phase, thus ensuring mutual proximity, which is a particularlyclear advantage if the active phase and the catalyst are solid and wouldthereby have poor mobility if freely distributed in the polymeric means.Finally, in the case where the porous material is a zeolite, the zeoliteitself can act as a catalyst (acid or basic according to Lewis and/orBroensted) for a wide class of reactions, thus supporting the reactionof the active phase with the gas to be sorbed, as explained below.

In FIG. 1 a system of the invention is shown, in a generic embodimentthereof. In this case, the system 10 is shown in the form of a shortparallelepiped in a broken-away view, but the system could have anyother shape, e.g., a ribbon, a drop, or could be directly formed on aninternal surface of the device whose atmosphere must be controlled, forexample in the form of a thin layer, or occupy recesses of this surface.

The getter system is comprised of a polymeric means 11, characterized bya low permeability to the gas to be sorbed, inside which powders 12 of aporous material are distributed. The means 11 may be formed of anypolymeric material poorly permeable to the gaseous species to be sorbed.Preferably, this polymer shows adhesive characteristics, so that it maybe fixed onto an internal wall of the final device without usingadditional adhesives.

The low permeability of the polymeric means 11 to gases also allows thepolymeric means to accomplish the function of a barrier to the inlet ofimpurities into the body of the same means, thereby limiting the amountof impurities that must be sorbed by the active phase, prolonging theefficacy of the getter system over time and consequently the life of thedevices in which such system is used. By low permeability is intended apermeability not higher than 1×10⁻¹² m_((STP)) ³·m²/bar·m³·s, where(m_((STP)) ³ stands for cubic meters of gas measured at standardtemperature and pressure.

Porous materials suitable for forming powders 12 useful for the purposesof the invention are, for example, the natural or synthetic zeolites,silicalites (i.e., substantially zeolites without aluminum),aluminosilicates other than zeolites, fullerenes, and metal-organicframeworks (better known in the field as MOF; see for example thearticle “Metal-organic frameworks: a new class of porous materials,” byJ. L. C. Roswell and O. M. Yaghi, published on-line in Microporous andMesoporous Materials, no. 73, pages 3-14, June 2004).

FIG. 2 schematically shows an enlarged sectional view of a particle 12.The particle of porous material shows pores 20, 20′, . . . , insidewhich one phase active in gas sorption is arranged. The active phase isrepresented in the form of deposits 21, 21′, 21″, . . . . In thedrawing, the most general case is shown, wherein the pores areessentially in the form of channels having a variable section (betweendifferent pores and also in different locations inside the same pore),reaching the surface of the particle 12, and the deposits 21, 21′, 21″,. . . , adhere to the internal walls of the pores. Alternatively, forinstance in the case of zeolites, the pores have dimensions that arerigidly fixed by the crystalline structure, which, as is known per se,may show cavities mutually connected through passages of reducedsection, and the active phase could be simply arranged in the cavities,without being bonded to the internal surfaces of the same.

FIGS. 3 a and 3 b schematically show the operation mechanism of thegetter systems of the invention. FIG. 3 a shows, in a further enlargedview, a detail of particle 12, and in particular a pore 20, inside whichdeposits 21, 21′, . . . of the active phase are present, while themolecules of the gaseous species to be sorbed are designated by 30.During their motion the molecules 30 contact the deposits 21, 21′, . . .and react with them, thus being fixed on or by the deposits, withdifferent mechanisms according to the nature of the components of thespecific coupled gaseous molecule/active phase. This situation is shownin FIG. 3 b by the “modified” deposits 31, 31′, . . . . In the case ofzeolites, as previously stated, the active phase could be present not inthe form of a deposit, but rather in the form of particles being“trapped” in the zeolite cavities, and the product of the reaction withthe molecules 30 will be, in turn, in the form of a species trapped inthe same cavities.

The chemical nature of the active phase depends on the species desiredto be sorbed. For instance, in the case the species to be sorbed isoxygen, the active phase can be formed of easily oxidizable metals, suchas the alkaline metals, alkaline-earth metals or other metals, such asiron, tin and copper; metal oxides having low oxidation states, such asmanganese or copper oxides; salts with phosphite or phosphonite anion;or easily oxidizable organic compounds, such as phenols, secondaryaromatic amines, thioethers, or aldehydes. In the case of carbonmonoxide sorption, it is possible to use deposits of metals, like nickelor iron, which form complexed species with this gas, or alkenes, aminesand ketones in the presence of lithium-based organometallic compounds.In the case of carbon dioxide, the active phase can be a hydroxide of analkaline or alkaline-earth metal. In the (unusual) case where it isnecessary to sorb nitrogen, inorganic materials can be used such aslithium, barium, or the compound BaLi₄, or porphyrins, namely,metallorganic molecules which have the ability of fixing this gas to thecentral metallic atom of the complex.

The most common and important case is however that of moisture removal.For this purpose, the active species can be selected from a widespectrum of materials, which work according to different sorptionmechanisms, as summarized in the following list:

materials adding water: to this group belong epoxides; organic moleculeswith double or triple bonds (activated); oxides of alkaline metals, ofalkaline-earth metals or of pseudo-alkaline-earth metals (i.e.,essentially nickel, zinc and cadmium); organic (e.g., phthalic) andinorganic (e.g., boric) anhydrides;

materials undergoing hydrolysis or nucleophilic substitution: to thisgroup belong, for instance, some alkoxides (e.g., of aluminum, Al(OR)₃),some halides, e.g., AlCl₃, acylic halides (and particularly chlorides)having the general formula RCOX (where X is a halogen atom), orcompounds forming carbocations;

materials reacting with water with dissociation thereof and withformation of either an oxide and a hydride or of a solid solution.Examples of these materials are iron in the case of reaction with water,whereas, in the case of hydrogen sorption, yttrium, palladium ormixtures thereof;

materials being solvated by water, such as magnesium sulphate, ormetallic centers present in zeolites, in order to compensate the missingcharge due to aluminum.

In a preferred embodiment, the getter systems of the invention have thefurther property of being transparent to visible radiation throughouttheir life, as previously described. In this mode, the systems of theinvention are suitable for application in the previously cited screensof the OLED type.

These preferred getter systems comprise:

an amorphous polymeric means having a low permeability to the gases tobe sorbed;

a powder of a porous material distributed in the polymeric means, withthe powder particles having a mean size lower than 100 nanometers; and

a phase active in the sorption of one or more gases in the pores of theporous material.

In this preferred embodiment, the components of the systems exhibit, asadditional characteristics, the fact that the polymeric means isamorphous, whereas the porous material dispersed in the polymeric meansis nano-sized, being formed of particles having a size on the order ofabout 100 nanometers or less. The reason for the first one of these twoadditional requirements is that polymers are transparent only ifperfectly crystalline or completely amorphous. Since it is essentiallyimpossible to obtain perfectly crystalline polymers, especially in thecase of the present invention where powder must be dispersed in themeans, it is necessary to resort to completely amorphous polymers. Thesecond requirement comes from the fact that particles having dimensionsof less than half the wavelength of visible radiation do not causeinteractions with the same, and thereby do not alter the transparency ofthe polymeric means.

Polymers suitable for manufacturing a low permeability and transparentmeans are, for example, polyvinylchloride (PVC), polystyrene (PS),polymethyl(meth)acrylate (PMMA), copolymers withacrylonitrile-butadiene-styrene (ABS), copolymerized cycloolefins,polysulfones, polyethersulfone (PES) and particularlypolyaryleneethersulfone, copolymers with polyvinyldenefluoride,copolymers with polyhexafluoroisobutylene, copolymers with polyethylene,copolymers with polyperfluorodimethyldioxole, chlorinated polyamides,polyimides (PI), fluorinated polyimides (FPI), polycarbonate (PC),polyethyleneterephthalate (PET), acrylic resins, epoxy resins,polyurethanes (PU), polytetrafluoroethylene (PTFE), and liquid crystalpolymers (LCP).

Generally, in order to obtain a low permeability means, the citedpolymers and their manufacturing processes are preferably selected fromthose allowing achievement of the minimum free volume of the polymericmeans, the minimum order and regularity of the polymeric chains, themaximum cross-link rate, the maximum packing density, and the minimuminteractions with the permeating species.

The systems of the invention may contain, in addition to the alreadycited components, additional elements improving some properties orsupporting the achievement of the same.

For example, inside the pores of the porous material catalysts may bepresent, capable of accelerating the reactions between the species to besorbed and the active phase. For example, in the case of sorption ofwater by unsaturated organic molecules by addition to a double or triplebond, the catalyst could be an acid or a base according to Lewis orBroensted; metals like platinum and palladium can catalyze the sorptionof hydrogen; other metals like nickel, iron, rhodium, ruthenium, copper,or silver can also catalyze a variety of reactions involving an organiccompound and a gas, both through the formation of coordination compoundsinvolving the organic compound and/or the gas, and through redoxmechanisms.

Other elements that may be added in order to reduce the permeability ofthe getter system are nano-sized particles formed of inorganicmaterials, such as silica, alumina, aluminosilicates, tungsten oxide,zinc oxide, tin dioxide, titanium oxide, and also particles commonlyknown in the art as “platelets” (see, for instance, the article “Polymernanocomposites: from fundamental research to specific applications” byH. Fischer, published in Materials Science and Engineering, vol. C 23(2003), pages 763-772). The function of the nano-sized particles is todelay the diffusion and improve the uniform distribution of theimpurities.

The systems of the invention may be produced by pre-impregnating theactive phase in the porous material, and then forming suspensions of theso impregnated porous material in the polymeric means, if this hassufficiently low viscosity. Alternatively, it is possible to prepare asuspension of particles of the impregnated porous material in a solvent,where it is possible to solubilize also the polymer. Suitable solventsdepend on the chosen polymer and are well known in organic chemistry.Examples of solvents are chloroform, acetone, dimethylformamide, anddimethylsufoxide for polyaryleneethersulfones; nitrobenzene andtrichloroacetic acid for PET. Alternatively, it is possible to form asuspension between the porous material pre-impregnated with the activephase and precursors of the polymer (e.g., oligomers or monomers whichwill form the polymer) and cause the polymer be formed in-situ, e.g. byradiating with UV radiation. In order to stabilize the suspensions, itis also possible to add suitable surfactants thereto, well known inorganic chemistry and not requiring further descriptions. The startingsolution (if this contains the polymer or its precursors), or the lowviscosity polymer inside which the powders of the porous material arealready present, may be poured into suitable molds, or directly in thefinal housing, for example onto a suitable internal surface of an OLEDscreen. Once the liquid mixture has been poured into the desiredhousing, it may be made to “solidify” (meaning as “solid,” in this case,a material having a very high viscosity, such as to maintain the givenshape) by extraction of the solvent, polymerization in-situ, or, if thelow viscosity was produced by maintaining the polymer in the meltedstate, by cooling.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. A getter system for sorption of at least one gas, comprising: apolymeric means poorly permeable to the at least one gas to be sorbed; apowder of a porous material distributed in the polymeric means; and aphase active in sorption of the at least one gas, wherein the activephase is dispersed in pores of the porous material, and the poorlypermeable polymeric means has a gas permeability value not higher than1×10⁻¹² m³(STP)m⁻³bar⁻¹m²s⁻¹.
 2. The getter system according to claim 1,wherein the porous material is selected from natural or syntheticzeolites, silicalites, aluminosilicates, fullerenes, and metal-organicframeworks.
 3. The getter system according to claim 1, wherein, when theat least one gas to be sorbed is oxygen, the active phase is selectedfrom easily oxidizable metals, metal oxides having low oxidation states,salts with phosphite or phosphonite anion, and easily oxidizable organiccompounds.
 4. The getter system according to claim 3, wherein the easilyoxidizable metals are selected from alkaline metals, alkaline-earthmetals or other metals selected from iron, tin and copper.
 5. The gettersystem according to claim 3, wherein the metal oxides having lowoxidation states are selected from manganese and copper oxides.
 6. Thegetter system according to claim 3, wherein the easily oxidizableorganic compounds are selected from phenols, secondary aromatic amines,thioethers, and aldehydes.
 7. The getter system according to claim 1,wherein, when the at least one gas to be sorbed is carbon monoxide, theactive phase is selected from nickel, iron, alkenes, amines, andketones, the ketones being in the presence of lithium-basedorganometallic compounds.
 8. The getter system according to claim 1,wherein, when the at least one gas to be sorbed is carbon dioxide, theactive phase is a hydroxide of an alkaline or a hydroxide of analkaline-earth metal.
 9. The getter system according to claim 1,wherein, when the at least one gas to be sorbed is nitrogen, the activephase is selected from lithium, barium, the compound BaLi₄, andporphyrins.
 10. The getter system according to claim 1, wherein, whenthe at least one gas to be sorbed is water, the active phase is selectedfrom: epoxides, organic molecules with double or triple bonds, alkalinemetal oxides, alkaline-earth metal oxides, oxides of nickel, zinc orcadmium, organic or inorganic anhydrides, compounds formingcarbocations, alkoxides, hydrolyzable inorganic halides, acylic halides,iron, yttrium, palladium, and magnesium sulphate.
 11. The getter systemaccording to claim 1, wherein the system is capable of maintainingtransparency on variation an amount of the at least one gas sorbed,comprising: an amorphous polymeric means poorly permeable to the atleast one gas to be sorbed; and a powder of a porous materialdistributed in the polymeric means, wherein particles of the powder havea mean size of less than 100 nanometers and a phase active in sorptionof the at least one gas in pores of the porous material.
 12. The gettersystem according to claim 11, wherein the polymeric means is selectedfrom polyvinylchloride (PVC), polystyrene (PS), polymethyl(meth)acrylate(PMMA), copolymers of acrylonitrile-butadiene-styrene (ABS),copolymerized cycloolefins, polysulfones, polyethersulfone (PES),copolymers with polyvinyldenefluoride, copolymers withpolyhexafluoroisobutylene, copolymers with polyethylene, copolymers withpolyperfluorodimethyldioxole, chlorinated polyamides, polyimides (PI),fluorinated polyimides (FPI), polycarbonate (PC),polyethyleneterephthalate (PET), polysiloxanes, and liquid crystalpolymers (LCP).
 13. The getter system according to claim 1, furthercontaining, inside the pores, catalysts capable of acceleratingreactions between the at least one gas to be sorbed and the activephase.
 14. The getter system according to claim 1, further comprising aload of inorganic material for reducing the gas permeability of thepolymeric means.
 15. The getter system according to claim 14, whereinthe load is placed in the polymeric means in nano-sized form.
 16. Thegetter system according to claim 13, wherein the catalyst is selectedfrom platinum, palladium, nickel, iron, rhodium, ruthenium, copper, andsilver.
 17. The getter system according to claim 13, wherein thecatalyst is an acid or a base according to Lewis or Broensted.
 18. Aprocess for preparation of the getter system of claim 1, comprising thesteps of: pre-impregnating the active phase in the porous material; andforming suspensions of the impregnated porous material directly in thepolymeric means.
 19. A process for preparation of the getter system ofclaim 1, comprising the steps of: pre-impregnating the active phase inthe porous material; forming a suspension of the impregnated porousmaterial in a liquid solvent for the polymeric means; dissolving in thesuspension the polymer intended to form the polymeric means; andremoving the solvent.
 20. The process according to claim 19, wherein thesolvent is selected from: dimethylformamide and dimethylsufoxide whenthe polymer is a polyaryleneethersulfone; nitrobenzene andtrichloroacetic acid when the polymer is PET.
 21. A process forpreparation of the getter system of claim 1, comprising the steps of:pre-impregnating the active phase in the porous material; forming asuspension of the impregnated porous material in a liquid solvent forprecursors of polymer intended to form the polymeric means; dissolvingthe precursors in the suspension; causing polymerization of theprecursors to take place in the suspension; and removing the solvent.22. A process according to claim 21, wherein the suspension isstabilized by adding a surfactant.